The present invention relates to a cathode material having high capacity, high output and high safety for a lithium ion secondary battery, and to a lithium ion secondary battery using it.
For the application of a lithium ion secondary battery to a battery for plug-in hybrid cars, it is necessary to decrease its cost, volume and weight and to have high output while high safety is maintained. For such purposes, cathode materials are required to have high capacity, high output and high safety.
In JP-A-2006-302880, cathode materials containing a nickel oxide or second lithium-nickel composite oxide are used on a surface of a lithium nickel composite oxide, and safety during internal short circuit is improved without hampering high rate characteristics at a low temperature of a lithium ion secondary battery. This cathode material has a high resistance since particles with high resistance are coated on a surface of a lithium nickel composite oxide. Therefore, a further investigation is required to attain the high output required for the battery for plug-in hybrid cars.
In JP-A-2006-351378, cathode materials are represented by a general formula: LivNi1-w-x-y-zCOwCaxMgyMzO2 (wherein, the element M contains at least one kind of an element selected from the group consisting of Mn, Al, B, W, Nb, Ta, In, Mo, Sn, Ti, Zr, and Y). In the cathode materials, Ca, Mg and M are more distributed on a surface layer part as compared with in the inside of the active substance particles, and the materials are used to improve the lifetime property. This cathode material has a high resistance since containing an element that is not involved in a reaction. Therefore, a further investigation is required to attain the high output required for the battery for plug-in hybrid cars.
In JP-A-2006-351379, there is used a cathode material containing at least one kind of compound containing an element selected from the group consisting of Mn, W, Nb, Ta, In, Mo, Zr, and Sn on a surface of a lithium nickel composite oxide and the lifetime property is improved. Also, this cathode material has a high resistance since containing an element that is not involved in a reaction. Therefore, a further investigation is required to attain the high output required for the battery for plug-in hybrid cars.
As can be seen the above discussion, in the above-described prior arts, a further investigation is required to attain the high capacity, high output and high safety required for the battery for plug-in hybrid cars simultaneously.